1. Field of the Invention
The present invention relates to a controller with leakage current protection of a diode and an operation method thereof, and particularly to a controller and an operation method thereof that not only can have lower cost, but can also quickly enter leakage current protection when a diode has a leakage current.
2. Description of the Prior Art
Nowadays, a flyback power converter is one of the most popular power converters, wherein operational principles of the flyback power converter are that the flyback power converter stores energy and a reverse bias is crossed on a diode coupled to a secondary side of the flyback power converter when a power switch of a primary side of the flyback power converter is turned on; and the flyback power converter releases the energy to the secondary side of the flyback power converter and a forward bias is crossed on the diode when the power switch is turned off. However, when the flyback power converter operates with a heavy load coupled to the secondary side of the flyback power converter for a period of time, a temperature of the diode is increased so that the diode may not block the reverse bias when the power switch is turned on, resulting in the diode having a leakage current during the power switch being turned on. As shown in FIG. 1, if the power switch is turned on and the diode blocks the reverse bias, because an impedance of the diode is higher, peaks WP of a voltage VD corresponding to an auxiliary winding of the flyback power converter are attenuated slowly when the power switch is turned off; and as shown in FIG. 2, if the power switch is turned on and the diode cannot block the reverse bias, the diode will have the leakage current, because the impedance of the diode is lower, the peaks WP of the voltage VD are attenuated quickly when the power switch is turned off, wherein IPRI shown in FIGS. 1, 2 represents a current flowing through the power switch.
When the diode has the leakage current during the power switch is turned on, the leakage current may make the temperature of the diode be increased continuously until the diode breaks down. In addition, when the temperature of the diode is increased continuously, the diode can burn down a printed circuit board where the diode is mounted, or can even burn down an adapter which the flyback power converter is applied to.
Therefore, the prior art utilize over-temperature protection to prevent the above mentioned burning-down conditions from occurring, but the over-temperature protection needs to be implemented by an additional circuit, resulting in cost of the adapter being increased. In addition, another prior art utilizes a specific diode to prevent the above mentioned burning-down conditions from occurring, but the specific diode can also make the cost of the adapter be increased. Therefore, the above mentioned solutions are not good choices for a designer of the flyback power converter.